The present invention relates to an expandable core for the production of injection molded parts, the core being of the type including a segmented sleeve which is disposed around a stationary core pin and is movable in the axial direction of that core pin, the axially parallel segments of the segmented sleeve being movable radially inwardly from an injection molding state, or position, to an umolding state, or position.
Expandable cores are used for the injection molding of plastic parts which have internal threads, tongues, internal grooves, notches and recesses, as well as perforations and other undercut shapes. During the molding process, the outer surfaces of the segmented sleeves of such a core present mold surfaces for a corresponding inner wall of the injection molded part.
If this inner wall includes undercut portions, or recesses, the segmented sleeve must be brought to a smaller diameter during the unmolding process in order to permit separation of the molded part and the core. Expandable cores of the above-mentioned type achieve this by effecting inward movement, or collapse, of the segments during axial movement of the sleeve along the core pin.
In the known expandable cores this takes place only incompletely.